The DVR set-top boxes can consume as much as 446 kilowatt-hours a year. The boxes are typically running because they are recording television shows while the owner is away from their home. There is at least one set-top box for every two television owners, according to the study.

An average home in the United States consumes around 10,896 kilowatt-hours of electricity per year. That means that the set-top box, which sits inconspicuously on top of most televisions without generating any noise, accounts for around 4 percent of an average U.S. resident’s electricity consumption. The device is usually running full steam, even though it is left unused around 66 percent of the time, according to the report.

That idle time costs consumers around $2 billion every year, according to the report.

More energy-efficient options are available, although not from U.S. manufacturers, according to the report. A U.K. manufacturer has created a set-top box that powers down into sleep mode — reducing its electricity consumption by half — when the device is not in use. The device powers up briefly every half hour to check if the owner has requested a new show to record through a smartphone, and then powers back down if it doesn’t have to record anything.

The report also suggests that manufacturers create more intelligent ways to program and use the set-top boxes — such as using smartphones to manage the devices instead of leaving them on all the time. It would tie set-top boxes into the “smart grid” — an electrical power grid that is managed by advanced computer algorithms to promote better energy efficiency and reduce electricity waste.

The report indicates that Energy Star, a government-backed program that encourages manufacturers to create energy-efficient appliances, should drop the hammer on cable companies that are distributing the set-top boxes. The next phase of the program, Energy Star 4.0, will have much stricter standards for energy efficiency.